1. Field of the Invention
This invention relates to an electromagnetic actuator for a motor vehicle starter head, also referred to as a starter contactor.
More particularly, the invention relates to a contactor for a motor vehicle starter, of the type that includes a movable magnetic core, which is displaced axially under the effect of a magnetic field created by a winding that comprises at least one electrical conductor wound around a body of a coil, and of the type that includes a fixed magnetic core which extends transversely to a front axial end of the winding, of the type in which the fixed core comprises a rear base portion which is received axially in the coil and which includes an axial through hole for passage through it of a movable contact plunger, and of the type in which the fixed core includes an annular front disc, which is assembled to the rear base portion, and which is mounted in a cylindrical seating in the contactor.
2. DESCRIPTION OF RELATED ART
In a known way, the magnetic field produced by the electrical conductor wound around the body of the coil of a contactor follows lines of force which are substantially axial inside the coil, and which are in the form of loops closed on themselves outside the coil.
In a known design, the fixed magnetic coil is generally a piece made of soft iron which ensures continuity of passage for the magnetic flux between the carcass of the starter and the movable core.
Thus the lines of force are closed on themselves in the immediate vicinity of the coil, which enables the output of the electromagnet to be increased and the electrical power consumed by the latter to be reduced.
Generally, fixed magnetic cores used in the manufacture of conventional starters are made in one piece, and are made by a conventional extrusion method.
A major disadvantage of these cores lies in the complexity of their geometrical forms, which makes them expensive to manufacture.
In order to resolve this problem, it has previously been proposed to make fixed magnetic cores in two parts, corresponding respectively to the rear base portion and the front disc of the fixed core. In this type of design, the rear base portion, which is of simple form, is obtained by extrusion or turning or centring, while the front disc is made by stamping out in the press from a thick metal sheet.
However, the thickness of the front disc, which is a constructional feature which is indispensable in order to give satisfactory guidance to the movable contact finger connected to the movable core, is such that its manufacture by a press-forming operation gives low rates of production and requires a high-powered press, which makes manufacture of the front disc an expensive operation.
In order to overcome these drawbacks, the invention proposes a fixed magnetic core of simplified manufacture.
With this in view, the invention proposes a contactor for a motor vehicle starter, of the type that includes a movable magnetic core which is displaced axially under the effect of a magnetic field created by a winding that comprises at least one electrical conductor wound around a body of a coil, and of the type that includes a fixed magnetic core which extends transversely to a front axial end of the winding, of the type in which the fixed core comprises a rear base portion which is received axially in the coil and which includes an axial through hole for passage through it of a movable contact plunger, and of the type in which the fixed core includes an annular front disc, which is assembled to the rear base portion, and which is mounted in a cylindrical seating in the contactor, characterised in that the front disc consists of a stack of laminations.
In accordance with other features of the invention:
the laminations are thin press-formed laminations; PA1 the laminations have means for clipping them to each other, and means for connecting them to the rear base portion; PA1 the means for connecting the laminations to the rear base portion comprise a centring hole formed in each of the laminations, which enables the stack of laminations to be force-fitted on a sleeve portion of the rear base portion; PA1 the axial length of the sleeve portion is equal to the thickness of the stack of laminations, with the front end of the sleeve portion being flush with the annular front face of the front endmost lamination; PA1 the stack of laminations has at least one peripheral axial groove, and the front endmost lamination has a radial lug which is formed by stamping close to the periphery of the front endmost lamination, whereby to receive an electrical earth conductor of the coil and, on being bent back, to retain the conductor mechanically on the front endmost lamination; PA1 the front endmost lamination has at least two fingers formed by stamping, which extend axially forward for fastening an electronic circuit board, especially by welding or brazing; PA1 the front endmost lamination is tinned so as to facilitate soldering of the electronic circuit board; PA1 the front endmost lamination has on its edge at least three points which extend radially outwards so as to penetrate the material of the cylindrical seating of a carcass of the contactor, in which the stack is fitted axially so as to ensure electrical contact between the stack of laminations and the carcass.